Background: Mastectomies are traditionally performed under general anesthesia (GA), often with the addition of regional anesthesia for post-operative pain relief. Thoracic paravertebral blocks (TPVB) had previously been described in the literature to be sufficient for intra-operative anesthesia as an alternative to GA. A 2021 literature review by Cochrane Library comparing paravertebral anesthesia (with or without sedation) to general anesthesia for patients undergoing oncologic breast surgery showed that TPVB could reduce post-operative nausea and vomiting (PONV), hospital stay, postoperative pain and time to ambulation. It also resulted in greater patient satisfaction compared to GA. The aim of this study is to demonstrate the efficacy of single-injection TPVB done under ultrasound guidance for patients undergoing breast cancer surgery without axillary node dissection. Hypothesis: Single-injection thoracic paravertebral block is non-inferior to multiple (3) injections for oncologic unilateral breast surgery anesthesia.

Methods: The current study is a prospective randomized controlled trial of patients undergoing oncologic breast surgery without axillary node dissection or immediate reconstruction. Patients will be randomized into two groups; thoracic paravertebral block (TPVB) single-injection or TPVB multiple (three) injections. Significance/Importance: Oncologic breast surgery performed under TPVB and sedation lowers the risks of post-operative nausea and vomiting, decreases peri-operative use of narcotics, decreases pain scores at rest and on mobilization and leads to better overall patient satisfaction when compared to GA. It also leads to shorter hospital stays. Most studies use multiple injections to perform the block. Even though the risks associated with TPVB are low (3.6 per 1000 surgeries), the single-injection technique could reduce the risks even more. One injection is also easier to perform and of shorter duration, leading to greater patient tolerance and less side effects related to blocks performance duration such as vaso-vagal reactions or general discomfort. To date, no studies have compared the efficacy of single-injection paravertebral block and multiple injection techniques as the main modality of anesthesia for breast cancer surgery.